UNDERHOOD LAMP OUTPUT CIRCUIT Short to Battery
The underhood lamp circuit is stuck at battery voltage instead of turning off properly, like a light switch that's jammed in the on position. This indicates a wiring short or relay failure preventing the lamp from being controlled correctly.
The ECU monitors the underhood lamp output circuit voltage and expects it to toggle between ground (off) and battery voltage (on) based on the underhood switch state. When the circuit remains shorted to battery voltage regardless of switch input, the ECU cannot control the lamp and sets this code.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Lamp Output Voltage | 0V (off) to 12V (on) with switch control | Constant 12V+ regardless of switch position |
| Circuit Control Signal | Responds to underhood switch transitions | No response; voltage stuck high |
Code B2490 is a low-severity fault. Your vehicle is generally safe to drive to a workshop for diagnosis. However, do not ignore it indefinitely — low-severity codes often indicate developing problems that become expensive if neglected. Book a diagnostic appointment within 2–4 weeks. If you notice any additional symptoms (rough running, power loss, unusual smells), treat it as higher priority.
Once the fault is repaired, B2490 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.
The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.